Location theory is concerned with the problem of selecting the best location in a specified region for a service facility such as a shopping center, fire station, factory, airport, warehouse, etc. The mathematical structure of a location problem depends on the region available for the location and on how we judge the quality of a location. Consequently, there are many different kinds of location problems, and the literature is filled with a variety of solution techniques. Many location problems involve emergency facilities such as hospitals, fire stations, civil defense, or accident rescue. As in the distribution situation, emergency vehicles must travel along a road network and the facility may be located either at an intersection or along some road segment. Other applications of location problems include locating switching centers in communication networks, computer facilities, bus stops, and mailboxes, public facilities such as parks and shopping centers, and military supply points.